Arsenic, which element symbol is As, is one of the fifteenth elements group and is broadly distributed in earth crust. Also, it is exposed as elemental substances in nature by volcanic activity, or it is artificially appeared on earth surface by mining of ores or fossil fuels. Since seawater contains 2 ppb arsenic, plankton and sea alga introduce arsenic from seawater and accumulate arsenic in themselves. Since arsenic is also accumulated in fish and shellfish that eat them, arsenic is introduced into our human body. Meanwhile, arsenic is toxic or harmful substance as typified by the arsenic milk incidents. It is said that a lethal dose of inorganic arsenic is approximately 2 mg per kilogram of human body weight, that is, 2 ppm. In addition, it is said that even an uptake of an ultratrace amount of arsenic less than the above amount causes symptom like a vomit or a stomachache or a diarrhea, etc., a hepatic function disorder or a paresis, etc. and that a chronic uptake causes a tumorigenicity or a nervous disorder. Accordingly, since an interfusion of arsenic ion into water is hazardous to life, arsenic is requested to be eliminated from food and drinking water that we take in.
In many communities, arsenic ion is detected at dangerous levels in public drinking water supplies even though arsenic is eliminated by treating water in a drinking water treatment plant. High arsenic concentrations in the drinking water have been recently reported from USA, China, Chile, Bangladesh, Taiwan, Mexico, Argentina, Poland, Canada, Hungary, and India, also Japan. In water, the most common valence states of arsenic are As(V), or an arsenate, which is more prevalent in aerobic surface waters, and As(III), or an arsenite, which is more likely to occur in anaerobic ground waters. In the pH range of 4 to 10, the predominant As (III) compound is neutral in charge, while the As (V) species are negatively charged.
A various kinds of methods to detect arsenic have been developed as follows. For example, there are High level analysis (X. Peng, G. S. Chen, Chin. J. Anal. Chem. 31 (2003) 38 and H. Matsunaga, C. Kanno, T. M. Suzuki, Talanta 66 (2005) 1287), Raman and Infrared spectroscopy C. Ludwig, H. J. Gotze, M. Dolny, Spectrochim. Acta Part A 56 (2000) 547 and C. Ludwig, M. Dolny, H. J. Gotze, Spectrochim. Acta Part A 53 (1997) 2363), ICP mass spectrometry V. Dufailly, L. Noel, T. Guerin, Anal. Chim. Acta 611 (2008) 134), Electrochemical analysis (R. Piech, W. W. Kubiak, J. Electroanal. Chem. 599 (2007) 59), Chemiluminescence analysis (C. Lomonte, M. Currell, M. J. S. Richard, Anal. Chim. Acta 583 (2007) 72), Atomic absorption analysis (J. Michon, V. Deluchat, R. A. Shukry, C. Dagot, J. C. Bollinger, Talanta 71 (2007) 47 and C. G. Bruhn, C. J. Bustos, K. L. Saez, J. Y. Neira, S. E. Alvarez, Talanta 71 (2007) 81), Atomic fluorescence analysis (X. Li, Y. Su, K. Xu, Talanta 72 (2007 1728)), and Chromatography (A. L. Lindberg, W. Goessler, M. Grander, B. Nermell, M. Vahter, Toxicol. Lett. 168 (2007) 310 and Y. C. Yip, H. S. Chu, C. F. Yuen, W. C. Sham, J. AOAC Int. 90 (2007) 284). Though these methods are certainly valuable and have individual advantages, it cannot be denied that they have some demerits. For example, though Zhu et al. disclose that a detection limit of As3+ in Atomic absorption analysis of hydride evolution is 0.04 ngl-1 in the detection of As using a dielectric-barrier discharge vaporizer (Z. L. Zhu, J. Liu, S. H. Zhang, Anal. Chim. Acta 607 (2008) 136), there is fear that this method may be influenced a great deal by temperature. Also, Vincent et al. disclose a detection of As by a collision cell technology ICP-MS system. (D. Vincent, N. Laurent, G. Thierry, Anal. Chim. Acta 611 (2008) 134.) This method is high sensitivity, but multi atomic interference formation is found in the collision cell. Though Heitland et al. disclose a high-speed detection of As in urine by High-performance liquid chromatograph (HPLC) ICP/MS (P. Heitland, H. D. Koster, J. Anal. Toxicol. 32 (2008) 308), this method is expensive, in addition, organic solvent used is a large quantity and toxic. Though Matsunaga et al. newly developed a detection method by bare eye of a small amount of arsenic in water-soluble sample, this method needs advanced conditions that are adequately controlled. Furthermore, a detection limit of As by this method is 1×10−6 mol dm−3 and the reaction is very slow.
A condensation method, a catalytic method and an adsorption method are known as methods for removing arsenic ion. As the condensation method, it is known that arsenic ion could be removed by an oxidation agglomeration using iron salts or polyaluminum chloride (PAC) (general expression: [Al2(OH)nCl6-n]m (here, 1<n<5, m<10)), as shown in Japanese Patent Publication H07-088482. It shows that As concentration could be reduced to 0.0001 ppm, which satisfies a value less than 0.001 ppm that is an effluent standard adopted in 1993 in Japan. As the catalytic method, Japanese Patent Publication H09-327694 shows that arsenic ion is reduced and removed by hydrogen aeration using catalysts supporting rhodium to alumina (rhodium content 5 weight %, made by Aldrich Inc.) as a catalyst. As the adsorption method, the methods shown in Japanese Patent Publication 2000-176441, Japanese Patent Publication 2005-000747, Japanese Patent Publication 2000-024647, Japanese Patent Publication 2005-046728 and Japanese Patent Publication H10-137504 are known. Japanese Patent Publication 2000-176441 shows that arsenic ion concentration could be reduced less than 4000 μmol/L by using a mesostructure material of zirconium oxide system {the pore diameter D=20 to 50 nm, the contained amount of hexadecyltrimethylammoniumbromide (HTAB) was 39 wt %, and the cross-sectional diameter of HTAB is 30 to 40 nm.} that contained sulfate ion as an adsorbent. Japanese Patent Publication 2005-000747 shows that As concentration of the solution filtrated using a filter consisted of a chelate fiber immobilizing N-methyl-D-glucamine to a fibrous cellulose powder (Chelest fiber is provided by Chelest corporation) was 0.1 ppm or less. Japanese Patent Publication 2000-024647 shows that As concentration could be 8 ppm in the example using the material supporting 50 mass % to 60 mass % oxide or hydroxide of rare-earth metal to γ-alumina carrier (the average pore diameter is 119 nm, the pore volume is 0.713 cm3/g, the surface area is 240 m2/g, and the occupied ratio of 90 to 200 nm pores to the total volume is 88%) as an adsorbent. Patent Publication 2005-046728 shows that As concentration could be 8 ppm in the case of using an aminopropyl group modified magnetic-particle as an adsorbent. Japanese Patent Publication H10-137504 shows that As concentration could be reduced till 9×10−7 mol/L by using a granular impregnation resin supporting 8 g bis(2-ethylhexyl)ammonium-bis(2-ethylhexyl)dithiocarbamate to 20 g polyacrylic acid ester resin.